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The febrile infant up to 60 days
In a young infant with fever (38.0°C or more rectally) the decision rests on age in days and on appearance: the younger the baby, the fuller the work-up — up to 21 days always urine, blood, lumbar puncture and admission.
Why it matters in the exam
This is a classic scenario in every paediatrics and emergency exam: an infant a few weeks old with fever and no source. The question tests the age pathways (8–21, 22–28 and 29–60 days), the meaning of inflammatory markers (procalcitonin, CRP, ANC) and when a lumbar puncture can be skipped. A standard distractor is "he has a cold, so no urine test is needed" — a viral infection does not exclude a UTI.
The most common bacterial infection at this age is a UTI, followed by bacteraemia and meningitis. An ill-appearing infant of any age gets a full work-up and antibiotics at once. Remember HSV too: in the first 21 days, and in any infant with vesicles, seizures, high liver enzymes or CSF pleocytosis, acyclovir is added.
When approaching the case, check three things in order: the exact age in days, the general appearance, and the urine and inflammatory-marker results. Together they place the infant on the right pathway and dictate whether a lumbar puncture, admission and which antibiotic are needed. An infant born preterm, recently given antibiotics or with a chronic illness does not fit the standard pathways and gets a stricter assessment.
Key points
- Fever in a young infant = 38.0°C or more rectally.
- Up to 21 days: urine, blood and lumbar puncture, admission and antibiotics — always.
- 22–60 days: the decision follows the inflammatory markers (procalcitonin, CRP, ANC).
- The most common bacterial infection is a UTI.
- Consider acyclovir for HSV in the first weeks or with suggestive signs.
Summary table
| Age | Work-up | Lumbar puncture | Decision |
|---|---|---|---|
| 8–21 days | Urine, blood culture, inflammatory markers | Always | Admission and intravenous antibiotics |
| 22–28 days | Urine, blood culture, inflammatory markers | If markers are abnormal; if normal — optional | Admission; home observation only under strict conditions |
| 29–60 days | Urine, blood culture, inflammatory markers | Not needed if markers are normal | Positive urine with normal markers: oral antibiotics and review within 24–36 hours |
| Any age, ill-appearing | Full work-up | Yes | Admission and immediate antibiotics |
| Abnormal markers (AAP 2021) | Procalcitonin above 0.5 ng/mL, CRP above 20 mg/L, ANC above 4000, temperature above 38.5°C | — | Moves the infant to the higher-risk pathway |
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Sources
- AAP Clinical Practice Guideline: Evaluation and Management of Well-Appearing Febrile Infants 8 to 60 Days Old, 2021 — Age-based pathways
- Nelson Textbook of Pediatrics, 22nd edition (2024) — Fever Without a Focus in the Neonate and Young Infant
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.